This invention relates to photographic systems, and in particular to a system for producing good quality still photographs using chroma-key processing.
There are many applications, such as Theme Park and Theater Event photography, where the capability of xe2x80x9ccutting outxe2x80x9d a subject from an image and pasting the subject onto a different background is desirable. This may be achieved by capturing an image of the subject against a colored background and processing the image such that where the background color occurs in the scene, it is replaced by a second image. This xe2x80x9cchroma-keyxe2x80x9d or xe2x80x9cblue screen imagingxe2x80x9d is a technique commonly used in television and film production. Additionally, by overlaying a third image, a three level composite image can be produced.
Although the use of chroma-key processing in video images for television or films, for example, results in a satisfactory end product, the loss of detail around a subject, which is not readily apparent to a viewer of video images, can occur. More particularly, the background color which acts as the xe2x80x9ckeyxe2x80x9d may be modified, for example as it diffuses through the hair of a subject, thereby making difficult the decision as to whether it constitutes the colored background or the subject. This can result in loss of hair detail and a colored xe2x80x9chaloxe2x80x9d effect on the final image. Further, false keying on the clothes of a subject, when the color of the clothes matches the key color, can also be a problem. Maintaining a low latitude to the color background color, as is desirable to minimize false keying on clothes, unfortunately exacerbates the problem associated with the halo effect around the hair of a subject.
The present applicant has already developed and launched a digital photographic system (known as the Photo Print System) which uses a charge coupled device (CCD) camera, a digital processor and a thermal printer for use in portraiture situations where the xe2x80x9cinstantxe2x80x9d production of high quality images is required. This system has the ability to produce prints with varying formats or packages and add theme borders or overlays. Examples where such a system might be applicable include xe2x80x9cMall imagingxe2x80x9d (e.g. photos with Father Christmas) and Special Events (e.g. a Graduation Ball). Control of the system is made very simple by employing a Touch Screen Monitor. Such a Photo Print System, without any chroma-key facility, was launched by the present applicant in the autumn of 1995.
The present invention relates to an improvement over the Photo Print System by using a chroma-key process to produce good quality still photographs from the output of a digital still camera. Further, a photographic system according to the present invention is sufficiently simple and robust to be used in many operating environments by unskilled operators. This operating situation contrasts significantly with that which exists in a television or film application, wherein the ambient light conditions and appearance of a subject can be entirely controlled.
In one aspect, the present invention provides a photographic system comprising a digital still camera for producing a first output signal, means for processing the first output signal with a pre-recorded second output signal to detect an object, and means for extracting and combining the detected object with a third image signal to produce a revised image signal wherein the means for processing adjust the camera output signal to a gamma value of about unity prior to processing with the prerecorded second output signal.
Advantageously, the photographic system comprises means for printing the revised image signal.
The first output signal may comprise the object against a selected background, which preferably consists of a single color. The pre-recorded second output signal may comprise a picture signal of the key color background. The processing means may be arranged to define the object of the first output signal. The third image signal may comprise a picture signal of the background image that is required for the object.
In another aspect, the present invention provides a photographic system comprising a digital still camera for producing an output signal, means for processing the output signal with a pre-recorded picture signal to produce a revised image signal and means for printing the revised image, wherein the means for processing uses chroma-key processing to insert a background picture signal into a key color-characterized region of a foreground picture signal and in which the means for processing adjusts the camera output signal to a gamma value of unity prior to the chroma-key processing.
As far as the applicant is aware, the use of chroma key processing in connection with the output from a digital still camera to produce still photographs is novel and was not in any way obvious when this invention was made due to the problems associated with the quality of images produced using the known chroma-key techniques.
This is a marked change from the television or film chroma-key processing systems, wherein a gamma value of about 0.4 is normally used. Further, if a gamma value of 0.4 were to be used in the chroma-key processing of an output from a digital still camera, a very poor quality revised image may result if ambient conditions change.
The means for processing preferably extracts and stores detail from the foreground picture signal prior to the chroma-key processing. By extracting and storing this information, the quality of the revised image can be improved following the chroma-key processing during which detail can often be lost. The detail from the foreground picture signal is preferably recombined with the revised image signal following chroma-key processing and prior to the printing of the revise image.
The detail from the foreground picture signal which is extracted and stored by the processing means is preferably limited to a peripheral region of a subject which is to appear in the revised image. This is because the loss of detail resulting from the chroma-key processing exists primarily around the periphery of the subject due to the merging of the key color background with the hair, for example, of the subject. Thus, the characteristics of the detail extracted can be more closely matched with those lost during the chroma-key process.
The periphery or xe2x80x9crimxe2x80x9d of a subject may be determined by means of a filter. For example, the filter may establish an area of perhaps 11 pixels wide around the subject periphery and will include areas which are fully enclosed by the subject, such as under an arm or clump of hair of the subject.
A photographic system is provided, including a digital still camera, which is arranged to use chroma-key processing. The camera produces a first output signal and processes this with a pre-recorded second output signal to detect an object. The detected object is extracted and combined with a third image signal to produce a revised image signal. Prior to processing with the prerecorded second output signal, the camera output signal is adjusted to a gamma value of about unity. This ensures that the camera is suitably robust for operation, which is independent of ambient light conditions.
The means for processing preferably includes a reference image store for receiving chroma characteristics, and preferably luminance characteristics, corresponding to the key color-characterized region of the foreground picture signal As will be appreciated, by storing this information when the photographic system is initially commissioned or set-up at a particular location, it is not necessary to obtain the information each time the digital still camera takes a picture of a subject. This is somewhat surprising, since ambient light conditions will vary depending on the time of day, for example, but a system according to the present invention automatically deals with such light variation to produce consistently good revised image pictures.
The chroma and/or luminance characteristics, which are stored in the reference image store, are preferably averaged over a 7 pixel by 7 pixel array. This averaging could, of course, take place over a larger or smaller number of pixels depending on the camera being used, but a 7xc3x977 pixel array average has been found to be sufficient to calibrate a practical system taking into account the camera noise, without resulting in excessive processing time.
The digital still camera preferably includes a charge coupled device array.
Further, a color filter array preferably overlays the CCD array.
In a particular embodiment, the color filter array may have a Bayer pattern of red, green and blue.
Preferably a cathode ray tube communicates with the digital still camera to display the output signal from the digital still camera. Such an arrangement enables an operator to view a picture taken by the camera, prior to the chroma-key processing of the picture.
Although the means for printing the revised image is preferably a thermal printer, any other appropriate apparatus may of course alternatively be used.
The color of the key color-characterized region of the foreground picture signal is preferably green. This is because a color filter array having a Bayer pattern has twice as many green pixels as red or blue and the green spectral response is broad, moving it closer to luminance, and has the lowest noise level.
In a particular application of the photographic system according to the present invention, a light source may be included to remove any shadow from behind a subject during preparation of the digital still camera output signal If a shadow does occur, it may affect the chroma and/or luminance characteristics of the key color-characterized region of the foreground picture signal, thereby resulting in the area of the shadow not being replaced by the pre-recorded background picture signal.